import math

def is_prime(n):
    if n <= 1:
        return False
    if n <= 3:
        return True
    if n % 2 == 0 or n % 3 == 0:
        return False
    limit = int(math.sqrt(n)) + 1
    for i in range(5,limit,2):
        if n % i == 0:
            return False
    return True

print(is_prime(11))
print(is_prime(20))

'''
def is_prime(n):
    if n <=1:
        return False
    for i in range(2,int(n**0.5) + 1):
        if n % i == 0:
            return False
    return True
    
print(is_prime(11))
'''